Viral Nanoparticles Donning a Paramagnetic Coat: Conjugation of MRI Contrast Agents to the MS2 Capsid

A nanoparticle magnetic resonance imaging (MRI) contrast agent was developed by conjugation of more than 500 gadolinium chelate groups onto a viral capsid. The high density of paramagnetic centers and slow tumbling rate of modified MS2 capsids provided enhanced T1 relaxivities up to 7200 mM-1s-1 per particle. A bimodal imaging agent was generated by sequential conjugation of fluorescein and Gd3+ chelate. These results illustrate the potential for engineering natural protein assemblies to address bionanotechnology applications.